Can you file a bug asking for that kind of API event?

I saw similiar things requested...check this out:
https://bugzilla.mozilla.org/show_bug.cgi?id=1232178

EDITED 05.09.2017:
I followed your link and saw it was marked as resolved.

As I see in the 'linked' bug, they won't implement the functionality. They see WebExt have to deal with the web, not the browser chrome :\

This webextensions thing is getting tiresome...almost nothing will work (I mean extensions, from before)

small, fast and useful

It does what it's supposed to do and makes managing my tabs easier.

I use this not only to pin tabs, but also to move them. Invoking the shortcut twice moves a tab to the front of the list.